Suzuki Carry 1.3. loses strength when climbing

I have a Suzuki Carry 1.3 van and the problem is that it remains, it loses strength, it does not pass the 80 km/hour some people tell me that it is dirty injectors, in addition the benzine filter comes together with the benzine pump and inside the pond and that this can be the problem. Others say they are the coils. They are 2 and one is for two spark plugs. The ignition is good when the engine is walking and has strength in slow marches but in speed it is staying.
The idea is not to change everything if you do not reach the exact point of the problem. So, friends to get all your wisdom and help me out of the problem. Thank you all

And in the end what did it have?
I have the same problem